ROCKVILLE, Maryland (CNN) --Montgomery County Police have issued a composite photograph of a second vehicle they are looking for as they attempt to close the net on the D.C.-area sniper.

Police Chief Charles Moose released the composite of a white box-type truck that witnesses have seen near four of the shooting locations.

Earlier Saturday, Spotsylvania County, Virginia, police linked the killing of a man shot Friday while pumping gas with the series of sniper attacks in suburban Washington which began on October 2.

The announcement brought the total number of deaths attributed to the sniper to eight. Two others have been wounded.

"The ballistics evidence has conclusively linked the shooting yesterday in Spotsylvania County to the other shootings in Virginia, D.C. and Maryland," Maj. Howard Smith of the Spotsylvania County Sheriff's Department said.

The victim of Friday's shooting was identified as Kenneth Bridges, 53, of Philadelphia, Pennsylvania. The co-founder of a marketing distribution company was in the area on a business trip.

"Ken was a loving husband, father of six children and an outstanding citizen of the Philadelphia community," friend Gary Shepherd said. "While no family should have to endure this type of tragedy, the Bridges family hopes that this killer is brought to justice as quickly as possible."

Smith said Bridges had been shot once in the upper left back.

Five people were killed in Montgomery County, Maryland, during a 16-hour period from October 2 into the next morning. A sixth sniper victim was shot dead the night of October 3 on a Washington street. On October 9, a man was shot and killed in Prince William County, Virginia.

Two other sniper victims were wounded, one on October 4 in Spotsylvania County, Virginia, and another on October 7 in Prince George's County, Maryland. (Trail of the sniper)

Moose, who is heading the sniper investigation, asked the public on Friday to watch for a white Chevrolet Astro-type minivan, with a ladder on top.

Witnesses near Friday's shooting reported seeing two people in a white van. Immediately after the shooting, traffic on all bridges leading from Virginia into Washington and Maryland was slowed to near gridlock as authorities scrutinized cars and their occupants at roadblocks.

"We actually funneled it into one lane of traffic," said Virginia State Police Col. W. Gerald Massengill.

State police ordered white vans to pull over, and questioned their occupants, but no suspects were taken into custody.

Law enforcement officers said they have a description of the two people reported inside the van being sought.

"We do have a number of leads, and from the scene this morning, we developed additional information that we'll be following up on, and hopefully will be productive," said Massengill.

In a related development, law enforcement oficials on Saturday put into effect a "sniper response plan."(Full story)

Public urged to look for strange behavior

Moose also suggested the public watch for behavior that is suspect: "Someone who was not at work during the incident, has not been keeping their schedule, has taken on some kind of attitude about the joy of all of these events, has taken on some kind of anger towards the police," he said, adding that anyone witnessing those behaviors should call the sniper tipline.

Police on Saturday confirmed that Kenneth Bridges, 53, is the latest victim of the sniper.

A Virginia state police officer was working an accident across the street from the gas station when Friday's shooting occurred.

"It probably took him less than a minute to get to the victim," Smith said.

"Obviously, with a uniformed trooper directly across the street, we're dealing with an individual that is extremely violent and obviously doesn't care," he added.

At the scene of Friday's shooting, police were seen carefully placing into a plastic bag a yellow piece of paper retrieved from across the street from the gas station, but it is not known if that paper had anything to do with the case.

Safety concerns over the shootings led authorities to cancel plans Saturday to administer the Scholastic Aptitude Test -- a college entrance exam -- at 10 Washington-area locations, affecting approximately 2,000 students.

Earlier in the week, authorities found a Tarot card and a shell casing near the site of a shooting at a middle school that critically wounded a 13-year-old boy.

That Tarot card -- the "Death Card" in the fortune-telling deck -- had the message "Dear Mr. Policeman, I am God." It is believed to be the only communication to law enforcement from the sniper.

Geographic profilers have been studying the locations of the sniper shootings in an effort to draw a picture of the sniper.

Three of the sniper shootings have targeted people filling their cars at gas stations, and three were near highway entrance ramps.

Friday's shooting occurred about 5 miles from where a 43-year-old woman was shot and wounded last Friday outside a Michaels crafts store, also in Fredericksburg. She was released from the hospital Tuesday. (Shooting victims)